ECT Sensor Resistance (Engine management system - EDC)

The ECM ECT sensor circuit consists of an internal voltage divider circuit incorporating an external negative temperature coefficient thermistor. As temperature rises, the resistance in the thermistor decreases, as temperature decreases, the resistance in the sensor increases. The output of the sensor is the change in voltage as the thermistor allows more current to pass to earth according to the temperature of the coolant. The ECM compares the signal voltage to stored values and compensates fuel delivery to ensure optimum driveability at all times. The engine will require more fuel when it is cold to overcome fuel condensing onto the cold metal surfaces inside the combustion chamber. To achieve a richer air/fuel ratio the ECM extends the injector opening time. As the engine warms up the air/fuel ratio is leaned off.

The inputs and outputs for the ECT are a reference voltage and an earth return circuit, both provided by the ECM. The ECT signal is measured at the ECM.

ECT Sensor Resistance

In the event of an ECT sensor signal failure any of the following symptoms may be observed: l Difficult cold start. l Difficult hot start. l Driveability concerns. l Temperature gauge reading does not accurately represent the coolant temperature.

In the event of ECT signal failure the ECM applies a default value of 80 °C (176 °F) coolant temperature for fuelling purposes. The ECM will also run the cooling fan when the ignition is switched on to protect the engine from overheating.